Derivatives of acetals of polyhydric alcohols are useful in several applications, including, for example, as nucleating or clarifying agents for polymer resins and as gelling and thickening agents for organic liquids. DBS-based compounds are useful in such applications.
Nucleating or clarifying agents have been used to reduce haze in articles manufactured from crystalline polyolefin resins. Representative acetals of sorbitol and xylitol, which have been employed as nucleating or clarifying agents, are described in Hamada, et al., U.S. Pat. No. 4,016,118, dibenzylidene sorbitols; Kawai, et al., U.S. Pat. No. 4,314,039, di(alkylbenzylidene) sorbitols; Mahaffey, Jr., U.S. Pat. No. 4,371,645, di-acetals of sorbitol having at least one chlorine or bromine substituent; Kobayashi, et al., U.S. Pat. No. 4,954,291, distribution of diacetals of sorbitol and xylitol made from a mixture of dimethyl or trimethyl substituted benzaldehyde and unsubstituted benzaldehyde. U.S. Pat. No. 5,049,605 to Rekers et al. discloses bis(3,4-dialkylbenzylidene) sorbitols. As an example of one type of clarifier, 1,3-O-2,4-bis(3,4-dimethylbenzylidene) sorbitol (hereinafter DMDBS), available from Milliken Chemical under the trade name Millad® 3988, provides clarification for target polypropylenes and other polyolefins.
Changes among various substituted groups in DBS-based compounds may have a significant impact upon the performance of the compound in plastics. In particular, substitution of various groups upon the benzyl ring portion(s) of DBS-based compounds may have a significant impact upon the suitability of such compounds as nucleating or clarifying agents. Accordingly, efforts in the past have been directed to modifying the substitution pattern of the benzylidene ring substituent(s).
Published patent applications US 2005-0239926A1 and US 2005-0239928A1 to Xie et al. disclose acetal-based compositions useful as nucleating or clarifying agents. These references disclose, in part, that dibenzylidene sorbitol derivatives substituted on the first carbon of the sorbitol chain are particularly effective clarifying agents.
The percent haze of polyolefin articles is a common measure of the level of clarity that a nucleating or clarifying agent imparts to polyolefin articles that employ such an agent. In general, a reduction of only a single percent (or even a fraction of a percent) in haze can be very significant in the industry. Thus, there is a continual endeavor in the plastic additives industry to find nucleating or clarifying agent compounds that will afford the lowest amount of haze. The leading commercial clarifying agent, Millad® 3988, provides about 7-8% haze in a 50 mils (1.27 millimeters) injection molded random copolymer polypropylene article. It has long been the objective of the industry to develop a clarifying agent that would provide reduced levels of haze under the same conditions and at the same concentration levels.
Low haze is not the only important factor in determining the suitability of a plastic additive. Poor thermal stability may cause undesirable yellowing and plate-out at high processing temperatures. Such yellowing is undesirable.
The nucleating or clarifying agent must not impart excessive undesirable taste to the plastic articles into which it is incorporated. Thus, nucleating or clarifying agents that provide reduced organoleptic problems or issues are desirable. “Organoleptic” refers to taste that undesirably may be transferred to a polymeric food or drink storage container by a nucleating or clarifying agent compound incorporated into the plastic.
These noticeable problems have created a long-felt need in the polyolefin clarifier industry to provide such compounds that do not exhibit these problems and provide excellent clarity for the target polyolefin articles themselves. To date, the best known compounds for this purpose remain those noted above.